Antibody titers to Epstein-Barr virus (EBV) virus capsid antigens (VCA) were significantly higher in patients with Hodgkin's disease (HD) than in controls. Herpes simplex virus (HSV) antibodies were also elevated in the HD patients as compared to controls, but the difference was not as significant as with the EBV VCA. Pair analysis, where the titer in each case was compared to that of matched control, demonstrated that the increased VCA titers were clearly due to patients, both male and female, with nodular sclerosis sub-type of HD. Levels of antibody to EBV VCA were studied in seven German patients with nasopharyngeal carcinoma. Four had titers equal or greater than 2560, one had a titer of 320, one had a titer of 160, and one had a titer of 80. Antibody levels to EBV early antigen were also studied. Two sera had titers of 10 or less, one had a titer of 80, one had a titer of 160, and one had a titer of 640. Nine sera from eight American patients with NPC were studied for antibody to EBV soluble antigen. Three of these sera were negative.